Calcium-dependent uncoupling of liver mitochondrial oxidative phosphorylation by a non-metabolizable long chain fatty acyl analogue was compared with uncoupling induced by in vivo thyroid hormone treatment. β,β'-Methyl-substituted hexadecane α,ω-dioic acid (Medica 16) is reported here to induce a saturable 20-30% decrease in liver mitochondrial ΔΨ, ΔpH and protonmotive force which proceeds in the presence of added Ca2+ to cyclosporin A-sensitive mitochondrial permeabilization. Ca2+-dependent uncoupling by Medica 16 was accompanied by atractylate-enhanced, bongkrekic-inhibited activation of mitochondrial Ca2+ efflux. The direct mitochondrial effect exerted in vitro by Medica 16 is similar to that induced by in vivo thyroid hormone treatment. Hence, the thyromimetic protonophoric activity of Medica 16 and the uncoupling activity of TH converge onto components of the mitochondrial permeabilization transition pore. Copyright (C) 2000 Elsevier Science B.V.
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